Effect of Mould Size on Compressive Strength of Green Concrete Cubes

This paper is aimed to evaluate the effect of mould size on compressive strength of concrete cubes made with recyclable concrete aggregates. Natural coarse aggregates were replaced with 50% recycled aggregates from old demolished concrete. Five different mould sizes were used to cast 420 concrete cubes using 1:2:4 mix and 0.55 water/cement ratio. In each size equal number of cubes was cured for 3, 7, 14 and 28-day. After curing, weight of cubes was determined followed by testing for compressive strength in universal load testing machine with gradually increasing load. From the obtained results the strength correction coefficients were computed keeping 28-day cured standard size cubes as control specimens. Also, numerical expression based on regression analysis was developed to predict the compressive strength using weight of cube, area of mould and curing age as input parameter. The numerical equation predicts the compressive strength very well with maximum of 10.86% error with respect to experimental results.

An eXtreme Gradient Boosting model for predicting dynamic modulus of asphalt concrete mixtures

Dynamic modulus (DM)—an important stiffness property and a basic input parameter in the design of flexible pavements—is often obtained through expensive, laborious, and time-taking laboratory tests, which can be subjected to human error as well. Predictive models are, therefore, developed in lieu of laboratory testing, enabling the estimation of DM values with some degree of error. Focussing on minimising this error in predicting the DM of asphalt concrete (AC) mixtures, this study proposes an eXtreme Gradient Boosting (XGBoost) approach for modelling DM. Sixteen AC mixtures are prepared in laboratory and tested for DM at different testing temperatures and loading frequencies. The data obtained from the laboratory test are divided into three categories: testing conditions, mix volumetric properties, and gradation, which served as the input to the XGBoost model. More specifically, testing conditions include four testing temperatures (4.4, 21.1, 37.8, and 54.4 °C) and six loading frequencies (25, 10, 5, 1, 0.5, and 1 Hz), mix volumetric properties entail optimum bitumen content, air voids, voids filled with aggregate and asphalt, stability and flow of a mix, binder type, and type of layer, gradation parameters consist of per cent passing of different sieve sizes. Several goodness-of-fit measures are employed combined with k-fold validation technique to robustly evaluate the performance of the developed model. Furthermore, the XGBoost model is compared with some well-known regression-based models as well as other machine learning approaches. The comparison analysis reveals that the XGBoost model outperforms its competing models from the literature by showing a higher degree of accuracy in predicting the observed DM values. Moreover, to further demonstrate the efficacy of the proposed XGBoost model, its transferability is tested for a completely new dataset, and the findings suggest that the model is able to capture the difference in mix properties and preparation type of the new dataset with a reasonable accuracy. In addition, the XGBoost model exhibits a superior performance in transferability analysis compared with its competing models. The findings of this study advocate the use of XGBoost approach for predicting DM values as well as in the design of flexible pavements in future studies.</p

Effects of partial replacement of fine aggregates with crumb rubber on skid resistance and mechanical properties of cement concrete pavements

This study analyses the skid resistance performance of rigid pavements by partially replacing fine aggregates with crumb rubber percentages in a laboratory setting. To achieve this objective, British pendulum testing is performed to examine the effects of crumb rubber on skid resistance in dry and wet conditions. In addition, mechanical properties such as compressive strength, tensile strength, and slump, are also investigated. Furthermore, a thorough literature review reveals that the relationship of skid resistance with mechanical properties is relatively scant, and a regression model is also missing that can predict skid resistance through these properties. To this end, this study presents empirical correlations, ascertaining a one-to-one relationship between skid resistance with mechanical properties. As different dosages of crumb rubber are used, this study also provides some guidelines on appropriate dosage of crumb rubber, keeping all the performance parameters in view. Findings of this study suggest that skid resistance is significantly enhanced when crumb rubber is added; however, it compromises the strength performance of rigid pavements. Therefore, an appropriate dosage of crumb rubber that balances them is required. Finally, correlations and models are evaluated and discussed in detail.</p

Using the Steady-State Chloride Migration Test to Evaluate the Self-Healing Capacity of Cracked Mortars Containing Crystalline, Expansive, and Swelling Admixtures

Interest in self-healing-crack technologies for cement-based materials has been growing, but research into such materials remains in the early stage of development and standardized methods for evaluating healing capacity have not yet been established. Therefore, this study proposes a test method to evaluate the self-healing capacity of cement-based materials in terms of their resistance to chloride penetration. For this purpose, the steady-state chloride migration test has been used to measure the diffusion coefficients of cracked mortar specimens containing crystalline, expansive, and swelling admixtures. The results of the present study show that the time to reach a quasi-steady-state decreased and the diffusion coefficients increased as the potential increased because of the potential drop inside the migration cell and self-healing that occurred during the test. Therefore, use of a high potential is recommended to minimize the test duration, as long as the temperature does not rise too much during the test. Using this test method, the self-healing capacity of the new self-healing technologies can be evaluated, and an index of self-healing capacity is proposed based on the rate of charged chloride ions passing through a crack

A binary logistic model for predicting the tertiary stage of permanent deformation of conventional asphalt concrete mixtures

Since the advent of Mechanistic-Empirical Pavement Design Guide (M-EPDG), characterisation of asphalt concrete (AC) mixtures using flow number remains the topic of interest for most of the literature. Consequently, many flow number models have been proposed in the literature, which only caters AC mixtures that attain the tertiary stage of permanent deformation (PD). The literature is devoid of any study that ascertain, whether an AC mix would attain the tertiary stage of PD or otherwise. As such, this study develops a binary logistic model as a function of volumetric and performance parameters of field and laboratory prepared AC mixtures using the standard maximum likelihood procedure. The logistic model specification is best suited to predict the mix probability of attaining the tertiary stage of PD. More specifically, an increase in air voids and percent passing sieve #200 in the mix and relatively low value of dynamic modulus translated into an increased probability of attaining the tertiary stage of PD. The field and laboratory mixtures are compared using the binary logistic model and a sensitivity analysis is also performed on the model. The comparison reveals the difference in both the type of mixtures, and suggests optimising and customising the laboratory mixtures to the field conditions

Effect of banana tree leaves ash as cementitious material on the durability of concrete against sulphate and acid attacks

The construction industry's rapid growth poses challenges tied to raw material depletion and increased greenhouse gas emissions. To address this, alternative materials like agricultural residues are gaining prominence due to their potential to reduce carbon emissions and waste generation. In this context this research optimizes the use of banana leaves ash as a partial cement substitution, focusing on durability, and identifying the ideal cement-to-ash ratio for sustainable concrete. For this purpose, concrete mixes were prepared with BLA replacing cement partially in different proportions i.e. (0 %, 5 %, 10 %, 15 %, &amp; 20 %) and were analyzed for their physical, mechanical and Durability (Acid and Sulphate resistance) properties. Compressive strength, acid resistance and sulphate resistance testing continued for 90 days with the intervals of 7, 28 and 90 days. The results revealed that up to 10 % incorporation of BLA improved compressive strength by 10 %, while higher BLA proportions (up to 20 %) displayed superior performance in durability tests as compared to the conventional mix. The results reveal the potentials of banana leave ash to refine the concrete matrix by formation of addition C–S–H gel which leads towards a better performance specially in terms of durability aspect. Hence, banana leaf ash (BLA) is an efficient concrete ingredient, particularly up to 10 % of the mix. Beyond this threshold, it's still suitable for applications where extreme strength isn't the primary concern, because there may be a slight reduction in compressive strength.Validerad;2024;Nivå 2;2024-04-23 (signyg);Funder: Taif University (TU-DSPP-2024-33);Full text license: CC BY-NC 4.0</p